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Urban wastewater treatment in Indonesia is limited, due to its high investment cost. To date, there are only 11 big cities that have centralized domestic wastewater treatment plant, such as in Jakarta, Tangerang, Bandung, Medan, Yogyakarta and Surakarta. There is also city sludge faecal treatment plant, like in Surabaya, Jakarta, Yogyakarta and Semarang. All the treatment process in these treatment plants is based on biological process, which are oxidation ditch (Tangerang and Surabaya), stabilization pond (Bandung) and extended aeration (Jakarta and Yogyakarta). Mostly, the biological treatment on the plants are malfunctioning, some of them because of operational capacity which cannot fulfill the design capacity. Yet, the effort of optimization only focuses on biological process aspect, while the hydraulic and physical aspects have a great influence to treatment performance. Research on modification of hydraulic aspect, both experimentally and by using computer simulation to improve treatment performance is needed.

It has been observed that the fidd biodegradation rates for soluble hydrocarbon plumes are significantly smaller than the aerobic rates observed in the laboratory. It is believed that this difference is related to the fact that in the field oxygen and hydrocarbon must be mixed before the biodegradation reaction can occur, and that the effective degradation rate is controlled by the actual, not mean, concentrations of oxygen and hydrocarbon. In this work, we present a conceptual model of oxygen-mixing limited biodegradation, which indicates that the effective degradation rate should depend on the cross correlation between the oxygen and hydrocarbon concentration fluctuations. This is followed by a development of a rigorous, field-scale model. I n t r o d u c t i o nIt is now well recognized that hydrocarbons dissolved in soil water, particularly those derived from gasoline, are relatively easily biodegraded when oxygen is present. There are a number of laboratory experiments reported in the literature to support this statement. There are also several detailed field studies that demonstrate passive biodegradation of soluble hydrocarbon plumes in aquifers [for example, Barker et al., 1987]. It has been observed that the field degradation rates are significantly smaller than the aerobic rates observed in the laboratory. It is believed that this difference is related to the fact that in the field oxygen and hydrocarbon must be mixed before the biodegradation reaction can occur. Since the time scale of mixing is typically longer than that of aerobic degradation, the overall rate of degradation is controlled by the mixing process.Passive biodegradation of soluble hydrocarbons is perhaps the most important mitigation process at a large number of field sites. To the best of our knowledge, all available modeling approaches to mixing-limited biodegrad~tion confuse the processes of spreading and mixing, in fact, the two processes are frequently thought to be equivalent. Recently, Miratles-Wilhelm et al. (1994) developed a new model of oxygentransport limited biodegradation. Their approach, however, does not consider one

Abstract. Paddy fields in the Rancaekek area, Bandung Regency-Indonesia, has been contaminated by textile wastewater. The area needs to recover back to its normal condition and function. Several compounds were found in the soil, such as Cu, Zn, Pb, Cd, Co, Ni, and Cr. Phytoremediation was selected as a site remediation strategy, which employs plants to remove non-volatile and immiscible soil contents. The objective of the study was to determine the ability of Equisetum debile to absorb Cu from the contaminated soil. Cu measurement was conducted by using the AAS (Atomic Absorption Spectrophotometer) method. The study has shown that Equisetum debile can absorb Cu concentrations of up to 25.3 ppm in 60 days after initial planting. However, the Enrichment Coefficient value (0.392) indicated that Equisetum debile was not efficient as a hyperaccumulator plant.